Positive displacement pumps and motors using the principle of an angularly offset rotary axis to cause a piston or plunger to rotate and reciprocate simultaneously, are well known. Examples of such pumps include:
U.S. Pat. No. 1,312,962, issued to Dourte, which describes a Valveless Pump providing a double action; but the mechanism involves a crankshaft and bevel gear arrangement, in which an upper connecting rod is reciprocated by the crankshaft and rotated by the bevel gears.
U.S. Pat. No. 3,266,432, issued to Stewart W. Wortley on Aug. 16, 1966, describes a Pump having a single cylinder with a piston centrally located therein. A valve is positioned on each side of the piston, with each valve alternatingly covering and uncovering an intake and a discharge port. Reciprocation of the piston is accomplished by an angularly adjustable swash plate.
U.S. Pat. No. 4,941,809, issued to Pinkerton, describes Valveless Positive Displacement Metering Pump. The device is similar to those disclosed in the same patentee's earlier '872 and '003 patents, but includes an angularly adjustable table to adjust the angular offset between the drive motor and the pump cylinder and plunger.
U.S. Pat. No. 5,246,354, issued to Guillermo P. Pardinas on Sep. 21, 1993, describes a Valveless Metering Pump With Reciprocating, Rotating Piston. The cylinder includes a single inlet port and two outlet ports, with the three ports being radially spaced apart about the cylinder. The single plunger includes a single relief on one side, which alternately communicates with the ports. The advantage of the Pardinas device is that the timing between the relief and the ports may be adjusted to provide accurate metering of fluid from the pump.
In U.S. Pat. No. 3,807,909, St. Clair describes a Pump For Dispensing Food in which dispensing of liquid or semi-liquid food products is controlled by a spool type valve equipped with a discharge nozzle. The pump also includes a product metering cylinder into which product is drawn during an intake stroke of a piston and from which product is expelled during a discharge stroke of the piston. While development of such devices has continued, they nevertheless have various limitations relating to complexity, reliability, cost, and ease of manufacture, particularly in such devices to be used for food or medicinal dispensing.